Dc voltage inverter

ABSTRACT

A capacitor operating at a temperature-autostabilized state, having a pair of exciting electrodes and a ferroelectric dielectric arranged therebetween. An AC generator is connected between the paired electrodes. The capacitor has output electrodes arranged in association with the first paired electrodes, and surrounded at least in part by one of them and an AC amplifier.

United States Patent Inventors Antonin Glanc Libochoviee; VaclavJanovec, Praha, both of Czechoslovakia Appl. No. 4,288 Filed Jan. 20,1970 Patented Oct. 19, 1971 Assignee Ceskoslovenska alrademie ved Praha,Czechoslovakia DC VOLTAGE INVERTER 14 Claims, 3 Drawing Figs.

US. Cl 310/8.l, 310/98, 317/247, 317/258, 317/259, 323/94, 330/7,331/116, 331/154, 331/163 Int. Cl 110lv 7/00 Field of Search... 310/80,8.1, 9.8; 323/94; 317/231, 258, 259, 247, 262; 331/154, 163; 330/7Primary ExaminerMilton O. Hirshfield Assistant ExaminerMark O. BuddAttorneysRichard Low and Murray Schaffer ABSTRACT: A capacitor operatingat a temperature-autombilized state, having a pair of excitingelectrodes and a ferroelectric dielectric arranged therebetween. An ACgenerator is connected between the paired electrodes. The capacitor hasoutput electrodes arranged in association with the first pairedelectrodes, and surrounded at least in part by one of them and an ACamplifier.

DC VOLTAGE INVERTER BACKGROUND OF INVENTION The present inventionrelates to contactless inverters and in particular to apparatus andmethod for converting DC voltages into corresponding AC voltages.

\ Inversion apparatus are commonly employed with AC amplifiers to detectand measure DC sources, particularly of very low voltage. Because theinverting mechanism is the most delicate and sensitive portion of suchapparatus it is important that it be accurate and consistent.

Existing contactlex inverters have many drawbacks and disadvantages. Forexample, theirinput resistance is not suffici'ently high; they aretemperature dependent, varying in input and consistency with changes intemperature; and require direct galvanic coupling between the input DCcircuit and the circuit of the resultant output, reducing thesensitivity of the apparatus, increasing the zero drift across theoutput and affect the input circuit to be measured.

It is an object of this invention to provide inverter apparatus which isfree of the mentioned drawbacks and disadvantages.

It is another object of this invention to provide inverter apparatuswhich is highly sensitive, easilyproduced, and easily employed over wideranges of input voltage.

' It isanother object of this invention to provide inverter apparatuswhich is free of temperature dependence and whose output is constantnotwithstanding changes in ambient temperature.

I It isstill a further object to provide inverter apparatus which iseasily adjustable for variable operating conditions.

These and other objects and advantages will be seen from the descriptionof the present invention contained herein.

SUMMARY OF INVENTION vAccording to the present invention there isprovided apparatus and a method derived in association therewith forltransforming a DC voltage into an AC voltage. Briefly the apparatuscomprises a capacitor having a pair of exciting electrodes and aferroelectric dielectric arranged therebetween,

an AC generator connected between the paired electrodes,

output electrodes arranged in association with the first pairedelectrodes, and surrounded at least in part by one of them and an ACamplifier. When an AC voltage of given frequency is impressed on thepaired electrodes the capacitor resonates mechanically so-that when a DCvoltage is applied across the BRIEF DESCRIPTION OF DRAWINGS In theaccompanying drawings:

FIG. 1 is a mechanical-electrical schematic illustration of inverterapparatus in accordance with the present invention,

FIG. 2. is a graph illustrating the shift of resonance peaks as afunction of temperature, and

FIG. 3 illustrates the operation of the apparatus of the presentinvention.

DESCRIPTION OF INVENTION The present invention makes use of techniquesdisclosed in the inventors U.S. Pat. No. 3,355,634 issued Nov. 28, 1967.

In that patent there is disclosed a capacitor and/or sensing deviceemploying a ferroelectric dielectric which is temperatureautostabilized. To avoid a lengthy disclosure here of redundant andrepetitious material, that patent is referenced herein as if it weremore fully set forth.

Turning now to FIG. 1 the present apparatus comprises an invertergenerally depicted by the numeral 1 formed of a dielectric 10 preferablymade in disk shape of a single crystal of triglycine sulfate, althoughother shapes and materials may be used. The dielectric 10 is provided onits lower face with a common electrode 11 and on its upper face with anexcitor electrode 12 of ring or annular shape. Both electrodes areradially coextensive with disk ltl within the center of excitorelectrode 12 and spaced therefrom is located an output electrode 13.

The electrodes I1 and 12 are respectively connected to the terminals ofan AC generator 2 providing a source of alternating current having avoltage E, and a frequency f (FIG. 2). 2). The electrode 13 is adaptedto be connected to one terminal 51 of the applied or detected source ofdirect current having a voltage E, via a choke or blocking resistor 6.The common electrode 1 1 is also connected to the second terminal 52 ofthe applied DC source.

The output electrode 13 is connected simultaneously through a couplingcapacitor 3, or suitable low-pass filter, to the first terminal of theinput end of an amplifier 4, which is also connected to the secondterminal 52 of the applied input DC source, in common with electrode 1].The amplifier 4 is provided with a pair of output terminals 41 and 42for connection to the AC circuit.

Located acrossthe ,output electrode I3 and the common electrode 11 is anadjustable or variable biasing source of DC voltage E, and a seriesconnected choke resistor 8 suppressing any undesired polarization of thedielectric material 10 and which when provided with opposed polarizationmay be used to bias and adjust the working point (i.e., relationshipbetween E, and E the apparatus by preventing shifting of the curve shownin FIG. 3.

Operatively, the AC generator 2 supplies a voltage E through thedielectric l0 creating a mechanical resonance therein between theexcitor electrode 12 and the common electrode 11 resulting in thepiezoelectric creation of an induced voltage across the output electrode13 and the common electrode 11. Simultaneously, if a voltage is passedfrom the input source E, the capacitor produces across the amplifier anAC voltage E of the desired magnitude proportional to the input E,,,.

Since the electrode 12 is ring shaped the heating region" or region ofdielectric loss lies coaxially about the periphery of the dielectric 10as indicated by the shaded portion 102. This meral 103 in FIG. 1, liesaxially with respect t the output electrode and constitutes the outputregion making use of the piezoelectric effect of the material. Thisoutput region is effected by the mechanical vibration of the dielectricand by the surrounding heating region and is raised in temperature tothe neighborhood of the phase transition of the ferroelectric materialand is maintained at that temperature during constant operatingconditions. In this transition thermal region the piezoelectriccoefficient (d) depends upon or responds directly to the voltage E Inaccordance with the'present invention, when the exciting voltage E, ismaintained constant, the AC output E has a magnitude directlyproportional to the magnitude of the applied DC voltage E, and afrequency which equals the second harmonic of the exciting frequency f.If the ambient temperature varies, the resonant peaks of the AC outputvoltage E shifts in a direction dependent upon the value of thefrequency f. That is the peaks at the low frequencies shift in onedirection while the peaks at the higher frequencies shift in theopposite direction. There is a certain critical frequency at whichnotwithstanding the change in temperature virtually no shift occurs.

The above is illustrated in FIG. 2 wherein the horizontal line frepresents the exciting frequencies, the vertical line represents theoutput AC voltage E and the dotted and full lines represent temperaturedependent outputs T and T,

respectively. It will be seen that at a frequency F, the curves of bothT and T coincide establishing a critical frequency at which no matterwhat the variation the ambient temperature takes there is no shift inthe output AC voltage E Consequently if the exciting frequency f ischosen as close as possible to this critical frequency f a the invertedor output voltage E becomes highly stabilized and virtually independentof temperature variation.

This desirable condition can be easily obtained by employing thecombination of adjustable biasing DC source 7 and the adjustableexciting or heating source 2. This is illustrated in FIG. 3 for anactual inverter employing a triglycine sulfate dielectric. Thehorizontal line represents the DC applied voltage E, and the verticalline represents the AC output voltage E To obtain the desired-operatingsituation the biasing voltage E is adjusted so that for a predeterminedinput voltage E the AC output voltage E is equal to 0 (zero). Thefrequency f of the exciting voltage E was then adjusted to be as closeas possible to the desired critical frequency f o rendering it virtuallyindependent of ambient temperature. As a result the curves T and T,corresponding to ambient temperatures 0 C. and 30 C. respectively areboth linear and coincident over the entire operating area.

It will thus be seen that the present invention provides DC inversionapparatus free of temperature sensitivity, providing a constant stableoutput. It will also be seen that the present apparatus is adjustableand operable over a wide range of operating conditions, so that it maybe made sensitive to very low DC voltages.

A number of modifications have been mentioned herein. Others will beobvious to those skilled in this art. For example the common electrode11 may be divided into two portions corresponding directly to theexcitor electrode 12 and the output electrode 13. The ring electrode 12may be modified to have merely an arcuate shape or be a split ring, theobject being that the electrode, at least partially, surrounds theoutput electrode. The changes and modifications suggested in theaforementioned patent may also be made here. Accordingly it is intendedthat this description be taken as illustrative only of the presentinvention and not as limiting thereof.

What is claimed:

1. lnverter apparatus for transforming a DC voltage comprising acapacitor having a pair of exciting electrodes and a ferroelectricdielectric arranged therebetween, an AC generator connected between saidpaired electrodes establishing an exciting region between saidelectrodes, output electrodes arranged in association with said pairedelectrodes and surrounded at least in part by said exciting regionforming an output region, means for applying a DC voltage to said outputelectrodes, and means for producing piezoelectrically at said outputregion an AC voltage maintained in a temperature autostabilized state inthe phase transition region of the dielectrio.

2. The inverter according to claim 1 wherein one of said pairedelectrodes and one of said output electrodes are commonly formed.

3. The inverter according to claim 2 wherein the other one of saidpaired electrodes is ring shaped and the other one of said outputelectrodes is located within the center thereof.

4. The inverter according to claim 3 including a source of DC voltageand a blocking resistor located between one terminal thereof and theother of said output electrodes.

5. The inverter according to claim 1 wherein said AC generator isadjustable to vary the frequency of its voltage.

6. The inverter according to claim 1 including a coupling capacitorassociated with said amplifier.

7. The inverter according to claim 4 including a second source of DCvoltage connected across the first source to bias the same.

8. The inverter according to claim 7 wherein said second DC voltage isadjustable.

9. The inverter according to claim 1 wherein one of said pairedelectrodes and one of said output electrodes are commonly formed, saidcommonly formed electrodes, one terminal of said AC generator and oneterminal of said AC amplifier being commonly connected one terminal ofsaid means for applying the DC current.

10. The inverter according to claim 5 including means for adjusting saidAC generator ro produce a frequency in the region of minimum resonancepeak shift as a function of temperature.

11. The method of transforming a DC voltage into an AC voltage employinginverter apparatus comprising a capacitor having a pair of excitingelectrodes and a ferroelectric dielectric arranged therebetween, an ACgenerator connected between said paired electrodes, output electrodesarranged in association with said paired electrodes, output pairedelectrodes and surrounded at least in part by one of them and an ACamplifier said method comprising the steps of creating an excitingregion between said paired electrodes, impressing an AC voltage thereon,and applying a DC voltage to said output electrodes and producingpiezoelectrically at said output electrodes an AC voltage proportionalto said applied voltage in a temperature-autostabilized state.

12. The method according to claim 10 wherein said impressed AC voltageis varied to provide a voltage having a selected frequency in the regionof minimum resonance peak shift as a function of temperature.

13. The method according to claim 12 including applying a biasing DCvoltage of opposed polarization across the first applied DC voltage.

14. The inverter according to claim 1 including an AC amplifierconnected to said output electrodes.

1. Inverter apparatus for transforming a DC voltage comprising acapacitor having a pair of exciting electrodes and a ferroelectricdielectric arranged therebetween, an AC generator connected between saidpaired electrodes establishing an exciting region between saidelectrodes, output electrodes arranged in association with said pairedelectrodes and surrounded at least in part by said exciting regionforming an output region, means for applying a DC voltage to said outputelectrodes, and means for producing piezoelectrically at said outputregion an AC voltage maintained in a temperature autostabilized state inthe phase transition region of the dielectric.
 2. The inverter accordingto claim 1 wherein one of said paired electrodes and one of said outputelectrodes are commonly formed.
 3. The inverter according to claim 2wherein the other one of said paired electrodes is ring shaped and theother one of said output electrodes is located within the centerthereof.
 4. The inverter according to claim 3 including a source of DCvoltage and a blocking resistor located between one terminal thereof andthe other of said output electrodes.
 5. The inverter according to claim1 wherein said AC generator is adjustable to vary the frequency of itsvoltage.
 6. The inverter according to claim 1 including a couplingcapacitor associated with said amplifier.
 7. The inverter according toclaim 4 including a second source of DC voltage connected across thefirst source to bias the same.
 8. The inverter according to claim 7wherein said second DC voltage is adjustable.
 9. The inverter accordingto claim 1 wherein one of said paired electrodes and one of said outputelectrodes are commonly formed, said commonly formed electrodes, oneterminal of said AC generator and one terminal of said AC amplifierbeing commonly connected one terminal of said means for applying the DCcurrent.
 10. The inverter according to claim 5 including means foradjusting said AC generator ro produce a frequency in the region ofminimum resonance peak shift as a function of temperature.
 11. Themethod of transforming a DC voltage into an AC voltage employinginverter apparatus comprising a capacitor having a pair of excitingelectrodes and a ferroelectric dielectric arranged therebetween, an ACgenerator connected between said paired electrodes, output electrodesarranged in association with said paired electrodes, output pairedelectrodes and surrounded at least in part by one of them and an ACamplifier said method comprising the steps of creating an excitingregion between said paired electrodes, impressing an AC voltage thereon,and applying a DC voltage to said output electrodes and producingpiezoelectrically at said output electrodes an AC voltage proportionalto said applied voltage in a temperature-autostabilized state.
 12. Themethod according to claim 10 wherein said impressed AC voltage is variedto provide a voltage having a selected frequency in the region ofminimum resonance peak shift as a function of temperature.
 13. Themethod according to claim 12 including applying a biasing DC voltage ofopposed polarization across the first applied DC voltage.
 14. Theinverter according to claim 1 including an AC amplifier connected tosaid output electrodes.